Telescopic booms are typically mounted to loaders and diggers in order to provide adjustable reach. Such booms are pivoted with respect to a chassis, which may be wheeled or tracked, and which is commonly self-propelled. In one example the boom is horizontally pivoted to the rear of a wheeled chassis so as to extend forwardly; a driver's cab is provided on the chassis at the side of the boom, and the long axis of the boom is offset to one side of the centreline of the chassis. Such a boom may be raised and lowered by hydraulic ram, and include one or more telescopic sections which may be advanced or retracted on demand to adjust the reach thereof.
It is desirable for the long axis of the boom to be parallel to the fore and aft centreline of the chassis. However the chassis mounting of the boom typically consists of a welded fabrication of many steel plate components, and it may be problematic to ensure that the pivot axis of the boom is perpendicular to the fore and aft centreline of the vehicle whilst maintaining other tolerances and dimensional requirements. In particular the pivot axis may be defined in separate steel plate components having bores which are independently machined, and line boring after fabrication may be impractical. Furthermore distortion of the fabricated assembly may occur during welding thereof.
It will be appreciated that any misalignment of the long axis of the boom is magnified at maximum boom extension, and that such misalignment becomes apparent after assembly of the boom to the chassis.
It would be desirable to provide yaw adjustment of the boom after manufacture and assembly of the device to which the boom is fitted.